There have already been described tube furnaces for the thermal cracking of hydrocarbon which comprise two opposing relatively small walls and two opposing relatively large walls which together define a furnace chamber through which pipes or tubes extend to conduct the hydrocarbon from an inlet side to an outlet side. The lateral walls of the furnace chamber are provided with burners supplied with fuel to generate the heat necessary for thermal cracking of the hydrocarbons within the tubes. The hydrocarbon to be cracked is conducted, via a feed pipe system through a convection zone lying above the combustion chamber and in which the hydrocarbons are preheated, to the furnace tube from which through the floor of the combustion chamber, the cracked hydrocarbons or cracking product is removed.
Thermal cracking of the hydrocarbons requires extremely high temperatures and short residence time as described in the aforementioned copending application. However, a further shortening of the residence time has been found to be impractical and it is, of course, desirable to operate with the highest operative temperature within the furnace. In fact, it is desirable to operate with temperatures as high as the material, from which the tubes and other furnace components are formed, can withstand.
In spite of the high temperatures and low residence times which are conventionally employed, it is found that the capital expenditures for tube furnaces for the hydrocarbon cracking and the operating cost thereof is not satisfactory.
Furthermore, the efficiency of conventional thermal-cracking tube furnaces leaves much to be desired.